This invention relates to a method of, and apparatus for, blow molding hollow articles of a thermoplastic material. More particularly, this invention relates to a method of, and apparatus for, blow molding hollow containers of a thermoplastic material.
The production of thermoplastic containers by shuttle blow molding is described, for example, in U.S. Pat. No. 3,614,807 (Lagoutte). In shuttle blow molding, two or more sets of blow molds, each of which is made up of a pair of mold halves that open and close relative to each other, are moved, in sequence, to engage an extruded tube of thermoplastic material at a moldable temperature, or a spaced apart plurality of such tubes in equipment used to simultaneously manufacture a plurality of containers in each mold set. Each mold set is then moved away to a station where the portion of the tube in the mold set is blown into its desired configuration, as determined by the configuration of a cavity that is defined by the halves of the mold set, the movement of each mold set according to the aforesaid ""807 patent involving a first motion coaxial with the extruded tube to stretch the tube to properly size it and/or to axially orient material therein. The halves of the mold set are then opened to permit removal of the blown article, and the mold set is then returned to grasp another section of the extruded tube or tubes for a repeat of the process. The mold sets of a given shuttle blow molding machine move in predetermined paths relative to one another so that sequential portions of the extruded tube are usually grasped by one or another of the mold sets, without the need to employ intermittent extrusion of the thermoplastic tube or tubes.
In the manufacture of containers by shuttle blow molding it has become popular to apply labels to the containers, by introducing a label or an opposed pair of labels into the open molds before the parison(s) are engaged thereby, by equipment that applies labels to the interiors of the open mold halves, and this equipment is generally described as in-mold labelling equipment. Known types of in-mold labelling equipment have the capacity to feed labels to the mold sets of a shuttle blow molding machine at a rate equal to the total of the production rates of all mold sets of the shuttle blow molding machine. Unfortunately, however, some of the known types of shuttle blow molding machines position the various mold sets at different positions from one another while containers are being blown therein. This, then, requires an in-mold labelling machine for each mold set, notwithstanding that the total capacity of the multiple in-mold labelling machines for a given shuttle blow molding machine far exceeds the molding capacity of all the mold sets of the machines. The use of an in-mold labelling device in connection with a shuttle blow molding machine is described, for example, in U.S. Pat. No. 4,769,205 (Oles et al.) and in U.S. Pat. No. 5,919,498 (Weber). Further, an in-mold labelling device in connection with an injection blow molding machine is described in commonly assigned U.S. Pat. No. 4,808,366 (Kaminski et al.), the disclosure of which is incorporated by reference herein.
Another disadvantage of known types of shuttle blow molding machines that applies even when the machine is not being used to apply labels to the containers in the mold is that article removal equipment must be provided for each mold set, because the article removal positions of the various mold sets differ from one another. A shuttle blow molding machine that employs four (4) mold sets is described in International Patent Application Serial No. PCT/US00/26497. However, there are many shuttle blow molding operations that do not require the full productive capacity of a four-mold machine.
Shuttle blow molding apparatus according to the present invention is made up of an extruder that continuously extrudes a tube of thermoplastic material of a suitable temperature for blow molding into a useful article, or a plurality of spaced apart tubes of such material, or blow head that continuously produces parisons of containers of such material. Such apparatus is particularly useful in producing containers for use in various packaging applications. In any case, the shuttle blow molding apparatus of the present invention also includes a pair of mold sets, or a superimposed plurality of pairs of mold sets, each set being made up of an opposed pair of mold halves that close and open with respect to each other, and the inside surfaces of the mold halves are configured so that the mold halves, when closed, define a cavity, or a plurality of cavities in the case of apparatus having a multi-tube extruder, in which an article is blown from a length of extruded tube to conform to the configuration of a cavity.
The shuttle blow molding apparatus of the present invention also includes apparatus for moving each mold set, in sequence, to an elevated position in which it grasps a length of extruded tube and then outwardly in a first transverse direction and downwardly to permit the other mold set to engage another length of extruded tube. The other mold set, with length(s) of extruded tube therein, is then also moved outwardly, in a second, oppositely directed direction, and also downwardly. The length(s) of extruded tube in each mold set is blown during movement of the mold set through a closed path back to its tube grasping position, which is the same for each mold set, for the start of another production cycle.
In moving back to their common tube grasping positions, the mold sets first move along spaced apart parallel horizontal paths to positions horizontally spaced from their tube grasping positions, and the lengths of extruded tubes in the mold sets are blown into containers or other hollow articles during this movement. At the conclusion of these horizontal movements, which occur at different times for each mold set, each mold set is then moved upwardly and inwardly to position it for return movement to its extruded tube grasping position. At the conclusion of this upward and inward movement, which sequentially positions each mold set at a common position, the mold set is opened and the container(s) therein removed, before return of the mold set to its tube grasping position. Thus, a single article take-out device can be used to withdraw blown containers from both mold sets because each mold set, in sequence, is at the same position for container removal. When it is desired to practice in-mold labelling with apparatus according to the present invention, it is only necessary to position a single in-mold labelling device at the tube grasping position of the mold sets to insert a label, or an opposed pair of labels, sequentially, into the mold sets while the halves of the mold set are still open and before length(s) of extruded tube(s) are grasped by the mold set.
Accordingly, it is an object of the present invention to provide an improved method of, and apparatus for, producing hollow articles of a thermoplastic material in a pair of mold sets that move, in sequence, in closed, quadrilateral paths relative to an extruder, each quadrilateral path having the same extruded tube engaging position and the same blown article removing position, but otherwise having different positions.
More particularly, it is an object of the present invention to provide a method and apparatus of the foregoing character in which finished articles can be removed from each of the mold sets at only a single position. It is also an object of the present invention to provide a method and apparatus of the foregoing character in which labels can be applied to the interiors of the open mold sets at a single location prior to the blowing of severed lengths of extruded tube into containers in the mold sets.
For a further understanding of the present invention and the objects thereof, attention is directed to the drawing and the following brief description thereof, to the detailed description of the invention and to the appended claims.